1. Field of the Invention
The present invention relates to a cartridge and an image forming apparatus.
2. Description of the Related Art
Hitherto, in image forming apparatus using an electrophotographic image forming process, there has been employed a process cartridge system in which photosensitive drums as image bearing members and developing rollers as developer carrying members are removable from an image forming apparatus main body. This process cartridge system allows users themselves to perform maintenance of the apparatus without an assist from service engineers. Thus, this process cartridge system has been widely used in image forming apparatus.
In this system, during image formation, the developing rollers are biased with a predetermined pressure toward the photosensitive drums. In this state, in a contact development system in which development is performed by bringing the developing rollers into contact with the photosensitive drums, elastic layers of the developing rollers are brought into contact with surfaces of the photosensitive drums with a predetermined pressure. Thus, when the process cartridges mounted to the image forming apparatus main body are not used over a long period of time, the elastic layers of the developing rollers may be deformed. As a result, a density unevenness of images may occur at the time of development.
Further, the developing rollers are held in contact with the photosensitive drums, and hence developer adhering to the developing rollers may be unnecessarily transferred onto the photosensitive drums. In addition, also when the photosensitive drums and the developing rollers are rotated in contact and rubbed against each other without performing development, deterioration of the photosensitive drums, the developing rollers, and the developer may be deteriorated.
In view of the circumstances, there has been proposed an image forming apparatus including a mechanism configured to act on the process cartridges so as to separate the photosensitive drums and the developing rollers apart from each other in the state in which image formation is not performed (Japanese Patent Application Laid-Open No. 2007-213025). In a longitudinal direction of each of the photosensitive drums of this image forming apparatus, a separation mechanism (part of the apparatus main body, which applies a force for separating the developing roller from the photosensitive drum) is provided on one end side, and an abutment mechanism (a mechanism configured to bring the developing roller into contact with the photosensitive drum) is provided on another end side.
However, in the related-art arrangement of the abutment mechanism (such as a pressurizing spring), a great force may be required for separating the developing roller apart from the photosensitive drum.
According to Japanese Patent Application Laid-Open No. 2007-213025, as illustrated in FIG. 12, a force of a pressurizing spring 203 is applied in the direction “h” about a rocking center 205 of a developing unit. This force causes the developing unit to rock, thereby bringing a developing roller 202 into contact with a photosensitive drum 201. Meanwhile, when a force from a mechanism of the apparatus main body is received by a receiving member 204, a force in a direction reverse to the direction “h” needs to be applied about the rocking center 205 against the force of the pressurizing spring 203. When the force in the reverse direction is greater, a motor with higher output needs to be selected as a drive source. As a result, increase in cost and size of the apparatus main body may occur.
In a cartridge including an abutment and separation mechanism for the photosensitive drum and the developing roller, there is a demand to reduce a force that is necessary for separating the photosensitive drum and the developing roller apart from each other.